Let's practise some scientific words you will find in your book.
2.METHODS OF STUDY THE EARTH INTERIOR (Earth's Layers)
The inner structure and composition of Earth consists of three layers :
the top layer called "crust" being about 35 to 60 kilometres thick;
the middle layer called "mantle" being about 2900 kilometres thick;
and the third layer "core" being about 3400 kilometres in radius.
The deepest well drilled into the earth so far is around 13 kilometres deep which is in the Kola peninsula in USSR. Since it is not possible to dig thousands of kilometres into the earth to study its structure and composition, therefore, an important question arises : How do scientists study the structure and composition ofinner parts of the Earth, without actually reaching these inner parts ? We shall now try to answer this question. The scientists study the structure and composition of the inner parts of earth by indirect methods. The two important methods which are used for this purpose are :
study of waves produced during the earthquakes on earth (earthquakes waves)
study of composition of meteorites which fall on the earth. Shall discuss both these methods one by one.
Study of Earthquake Waves
One of the most important methods to find out the structure and composition of inner parts of earth is to study the waves produced by earthquakes. Earthquakes are caused byfracturing and slipping of rocks inside the earth. The waves produced by earthquakes pass through the various regions of earth and emerge at its surface with valuable information about the physical properties of the inner regions of the earth through which they pass. The strength and speed of the earthquake waves depend on the nature, density, and physical state (solid or liquid) of the regions of earth through which they pass. The recording and analysis of the earthquake waves or vibrations is done at various "seismic stations" which have been established in different places of the world.
The study of earthquake waves tells us that as we go down the earth[2] ,
the density increases gradually and reaches its maximum value in the core.
The study of earthquake vibrations also tells us that the core of the earth is mainly made up of a liquid (molten iron).
Study of Composition of Meteorites
Another idea about the composition of earth comes from a study of the composition of meteorites. Meteorites are the chunks of matter which some time fall to the earth from outer space, and are supposed to be made up of the same matter as that of other planets (including earth).
There are two types of meteorites : one made of silicate stones and the other made up of iron. Since the earth is supposed to have the same composition as meteorites, therefore, we conclude that just as the meteorites are made up of two types of materials, silicate stones and iron, in the same way, the earth is made up of same two materials : the mantle being made up of silicate rocks and the core of earth made up of iron.
In fact, since the meteorites are supposed to contain different elements in the same proportion as the planets, so a study of the composition of meteorites actually tells us indirectly as to how much of each element should be present on earth. Knowing the composition of surface rocks of the earth (which can be found out by analysis), and the complete composition of whole earth (as disclosed by meteorites), we can easily find out the composition of deep, inaccessible regions of the earth.
La tomografía sísmica es una técnica relativamente nueva que usa ondas sísmicas para medir variaciones muy pequeñas en la temperatura dentro del manto. Ya que las ondas se mueven más rápido a través del material frío y más despacio a través del material caliente, las imagenes que los científicos reciben les ayudan a 'ver' el proceso de convección en el manto.
El movimiento de las placas está relacionado con la convección por todo lo ancho del manto. Inicialmente dicha convección se pensó limitada a la astenosfera pero la moderna técnica de "tomografía sísmica" (que detecta zonas de mayor y menor temperatura) demuestra que la convección afecta a todo el manto.
1. AUDIO tracks for this unit
2.METHODS OF STUDY THE EARTH INTERIOR (Earth's Layers)
The inner structure and composition of Earth consists of three layers :- the top layer called "crust" being about 35 to 60 kilometres thick;
- the middle layer called "mantle" being about 2900 kilometres thick;
- and the third layer "core" being about 3400 kilometres in radius.
The deepest well drilled into the earth so far is around 13 kilometres deep which is in the Kola peninsula in USSR. Since it is not possible to dig thousands of kilometres into the earth to study its structure and composition, therefore, an important question arises : How do scientists study the structure and composition of inner parts of the Earth, without actually reaching these inner parts ? We shall now try to answer this question.The scientists study the structure and composition of the inner parts of earth by indirect methods. The two important methods which are used for this purpose are :
- Study of Earthquake Waves
One of the most important methods to find out the structure and composition of inner parts of earth is to study the waves produced by earthquakes. Earthquakes are caused by fracturing and slipping of rocks inside the earth. The waves produced by earthquakes pass through the various regions of earth and emerge at its surface with valuable information about the physical properties of the inner regions of the earth through which they pass.The strength and speed of the earthquake waves depend on the nature, density, and physical state (solid or liquid) of the regions of earth through which they pass. The recording and analysis of the earthquake waves or vibrations is done at various "seismic stations" which have been established in different places of the world.
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donde K es el módulo de incompresibilidad,
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To understand these curved paths fllowed by seismic waves
look at the following document
Earthquakes: waves and location (video)
The study of earthquake waves tells us that as we go down the earth[2] ,
- Study of Composition of Meteorites
Another idea about the composition of earth comes from a study of the composition of meteorites. Meteorites are the chunks of matter which some time fall to the earth from outer space, and are supposed to be made up of the same matter as that of other planets (including earth).There are two types of meteorites : one made of silicate stones and the other made up of iron. Since the earth is supposed to have the same composition as meteorites, therefore, we conclude that just as the meteorites are made up of two types of materials, silicate stones and iron, in the same way, the earth is made up of same two materials : the mantle being made up of silicate rocks and the core of earth made up of iron.
In fact, since the meteorites are supposed to contain different elements in the same proportion as the planets, so a study of the composition of meteorites actually tells us indirectly as to how much of each element should be present on earth. Knowing the composition of surface rocks of the earth (which can be found out by analysis), and the complete composition of whole earth (as disclosed by meteorites), we can easily find out the composition of deep, inaccessible regions of the earth.
The Earth's magnetic field
PLATE TECTONICS with images
Plate tectonics: animations
Hot spots
PalaeomagnetismEarth 200 million years from now
TECTÓNICA DE PLACAS DESDE RECURSOS EN ESPAÑOL
La tomografía sísmica es una técnica relativamente nueva que usa ondas sísmicas para medir variaciones muy pequeñas en la temperatura dentro del manto. Ya que las ondas se mueven más rápido a través del material frío y más despacio a través del material caliente, las imagenes que los científicos reciben les ayudan a 'ver' el proceso de convección en el manto.
El movimiento de las placas está relacionado con la convección por todo lo ancho del manto. Inicialmente dicha convección se pensó limitada a la astenosfera pero la moderna técnica de "tomografía sísmica" (que detecta zonas de mayor y menor temperatura) demuestra que la convección afecta a todo el manto.
Tres simulaciones para la convección en el manto...
http://www.bioygeo.info/Animaciones/Conveccion1.swf
http://www.bioygeo.info/Animaciones/Conveccion2.swf
http://www.bioygeo.info/Animaciones/Conveccion3.swf
Flash cards for reviewing
Another set of flash cards
http://en.wikipedia.org/wiki/Seismic_wave